Rolling element bearings are typically manufactured with a certain amount of initial radial clearance between the rolling elements and the inner and outer bearing races. When these types of bearings are incorporated into machines requiring high system rigidity, accuracy, and repeatability, such as machine tools or cutting heads for cloth cutting machines, it may become necessary to minimize or eliminate the radial play in the bearings. This is usually accomplished by shifting the inner and outer bearing races relative to each other, a technique referred to by those skilled in the art as preloading the bearings.
One means of preloading two rolling element bearings, is to purchase the bearings as a matched set from the manufacturer. A matched set of bearings has a predetermined preload attainable by mounting the bearings adjacent to one another on a shaft and pushing the inner and/or outer bearing races together, thereby establishing the preload. The inner bearing races are generally pushed together using a standard bearing locknut and lockwasher mounted on an externally threaded section of the shaft. The bearing lockwasher includes a plurality of external tabs and an internal tab that slides in a keyway machined in the shaft. With the lockwasher engaging the inner race of one of the bearings, and the internal tab positioned in the keyway, the bearing locknut is threaded onto the shaft and tightened against the bearing lockwasher until the inner races of both bearings touch, thereby preloading the bearings. The locknut is then further tightened against the bearing until one of the external tabs in the lockwasher aligns with a slot in the locknut. The external tab on the lockwasher is then bent into the slot in the locknut and the combination of the internal tab being positioned in the keyway on the shaft and the external tab being retained in the slot on the locknut prevents the locknut from loosening during operation of the machine in which the bearings are installed.
A difficulty associated with the above-described method of preloading bearings sometimes occurs where very high rotational speeds are involved. In these cases, machining the keyway in the shaft for the internal tab of the lockwasher can cause the shaft to become unbalanced thereby increasing the level of vibration in the shaft. Another difficulty sometimes encountered occurs when there is insufficient material in the shaft, such as when the shaft contains a bore, to accommodate the keyway for the internal tab of the bearing lockwasher.
Another method used to preload at least two bearings is to incorporate spring washers, such as wavy or belleville-type washers. The washer(s) is placed over the shaft and engages the inner race of a bearing, a nut is then threaded onto the shaft and tightened against the spring washer which in turn urges the inner races of the bearings together and maintains force against the nut to prevent the nut from loosening. A problem associated with this method of preloading bearings is that the sizes and stiffness of commercially available washers is limited. Therefore, a properly sized washer may be unavailable, or it may be necessary to utilize several spring washers stacked one-on-top-of-the-other to obtain the desired preload. This requires that additional space be provided in the bearing assembly to accommodate the additional washers.
Based on the foregoing, it is the general object of the present invention to provide a bearing assembly that overcomes the above-described drawbacks of prior art bearing assemblies.
It is a more specific object of the present invention to provide an assembly including preloaded bearings wherein bearing locknuts, lockwashers, or spring washers are not needed.